Joining agent for joining ceramic with electric joining method

ABSTRACT

Described in a joining agent for joining electrically ceramic bodies by heating the joining agent inserted at the parts to be jointed between the ceramic bodies with an electric current flowing predominantly through the joining agent at high temperature. The joining agent is superior in the wetability and reactivity with the ceramics to ensure the joint part strength. The joining agent includes, as an electric conductor, an electric conductive component made of an ion conductor consisting of fluoride, chloride, and/or oxide, which forms carrier ions by the pre-heating and has an electric conductivity higher than that of the ceramic body at the electric current supplying time. During the supplying electric current to time, the joining agent has the electric resistance increased gradually at the molten state of the joining agent by decreasing the density or the mobility of the carrier ions. After the electric heating, the joining agent is changed into a composition having a high electric resistance and hence the electric current path moves smoothly.

BACKGROUND OF THE INVENTION

Previously, there has been disclosed various kinds of joining agents,such as inorganic solder comprising various oxides, fluorides andvarious metal solders comprising various metals for joining ceramicbodies to each other. For example, a joining agent composed of powdermixture of CaF₂ and kaolinite is applied to parts to be joined ofsilicon nitride ceramic plates and then heated at 1400° to 1500° C. infurnace to obtain jointed ceramics by a reaction of the joining agentand the silicon nitride ceramic (Japanese patent application,32084/1983). The use of the CaF₂ is in a purpose that the CaF₂decomposes thermally at a high temperature and produces F₂ gas whichcorrodes or eats away the surface of the ceramic. As a result, thereaction product between calcium and kaolinite promotes the reaction ofthe joining agent with the ceramics. When the joining agent is selectedto be in a good wetability and a high reactivity with the ceramic, thejoint part between the ceramic bodies are completed upon heating thejoining agent at a temperature higher than its melting point. Aconventional heating method is to heat the whole of ceramics with thejoining agent in the furnace at an joining temperature to achieve thejoining. When the ceramic body in a large size or a long size isjointed, it is necessary to use a large furnace or to take a long timefor heating up or cooling down. This results in the problem such as thelimitation of the equipment and an increase in the equipment cost orrunning cost. Further, the higher joining temperature may cause thethermal degradation of the ceramic body. Therefore, the problem occurswith the application field requiring the thermal resistance. Since theheating method to heat the whole of the ceramic body with the joiningagent has various problems as mentioned above, it is desirable toachieve an joining method to heat partially only the part to be jointed.In order to solve the problems, U.S. Pat. No. 4,724,020 has reported oneof electric joining methods for the ceramic bodies.

The electric joining method is carried out in the following way: Theplanes to be jointed of ceramic bodies are applied with an joining agenthaving an electric conductivity at a high temperature and are pre-heatedby a gas flame to a temperature more than about 800° C. in advance. Ahigh voltage is applied across a pair of electrodes to supply electriccurrent to the joining agent. Then the joining agent is heated by theJoule heat and is melted to complete the ceramic joining through thereaction between the joining agent and the ceramics.

PROBLEM TO BE SOLVED BY THE PRESENT INVENTION

The electric joining method mentioned above has an advantage to decreasethe joining cost including the equipment cost and running cost even withthe large size or the long size ceramic bodies and to suppress thethermal degradation of the ceramic material. However, the electricjoining method has the following disadvantage: The conventional joiningagent used in a furnace is required only to satisfy the wetability andthe reactivity with the ceramics. On the other hand, the joining agentused in the electric joining method must have an electric conductivityat a high temperature in addition to the above properties because thejoining is completed by supplying electric current to the joining agent.Accordingly, the joining agent in the conventional type using a hightemperature furnace is not always applicable for the electric joiningmethod. It is necessary to develop the joining agent suitable for theelectric joining method.

U.S. Pat. No. 4,724,020 reported the joining agent applicable for theelectric joining method, which has such an electrical conductivity thatpermits the electric current of several 10 mA to flow under the voltageof 1,000 to 10,000 V at a temperature higher than 800° C. As a practicalmatter, there is disclosed such a joining agent includes, as a mainconstituent, glass comprising kaolinite, Al₂ O₃, and SiO₂ and, as anadditive, oxide, sulfide or chloride of copper, nickel, manganese,indium, molybdenum, or zinc, or oxide of rare earth material such aslanthanum, indium, vanadium, holmium and yttrium, or metal such asmolybdenum, manganese, tungsten, iron, copper, silver, nickel, tin andzinc, or fluoride such as calcium fluoride and sodium fluoride. Thejoining agent having no electrical conductivity is added with a materialhaving an electrical conductivity such as carbon, fluoride, glass, metaloxide and rare earth materials.

However, it is found through the practical use by the inventors the factthat the joining agent having only the electrical conductivity and thereactivity with the ceramics does not always result in a formation ofgood joint. For example, an joining agent can have a metal powder as anelectrical conductor added into glass and permits the electric currentto flow therethrough. However, the electric current localizespredominantly at the metal powder portion. As a result, the part to bejointed is not heated uniformily and is not formed into a good joint.Especially, there is a big problem with the ceramic body in a long sizeto be jointed. Therefore, it is found that the joining agent providedonly with the electric conductivity is not sufficient for executing theelectric joining method.

As a result of the inventive investigation, the present inventors havenoted that it is necessary to develop a joining agent to permit theelectric current path to move smoothly with a movement of the electrodewhen the ceramic part is jointed by an electric joining method. It hasbeen known in the present technical field that the joining agent hasgenerally an electrical conductivity in a positive characteristic andmakes it difficult to move the electric current path with the movementof the electrode. Against the above information, the present inventorshave found that there may be an joining agent to permit the electriccurrent path to move with the movement of the electrode afterinvestigation of heating mechanism with various joining agents.

Referring to FIG. 1 showing a time variation in the electric resistanceof the joining agent, an increase in the voltage of the electric sourcecauses initially a slight electric current (referred to "initial drivingcurrent" hereinafter) to flow through the joining agent in the firstrange I. At the next step, the electric current increases rapidly at agiven value of the voltage and subsequently the load voltage decreasesrapidly in the second range II. After that, at a range where theelectric current is a constant value, the load voltage graduallyincreases, that is, at this range, the joining agent changes in thecomposition and is in a higher electric resistance (this range isreferred to the third range III hereinafter). Therefore, followed withthe movement of electrode or even without any movement of electrode, theelectric current path moves sequentially to an area in a lower electricresistance from an area in a higher electric resistance. That is,without any external force, the electric current path tends to be madeautomatically at an area for flowing of electric current and thus movevolontarily to any lower electric resistance areas from higher ones.Finally, thereby the reaction between the joining agent and a pair ofceramic bodies proceeds sufficiently to join the ceramic bodies inaccordance with the change in the composition into a higher electricresistance.

Accordingly, an object of the present invention is to provide an joiningagent to change in the composition to a high electric resistance andthereby the load voltage increases gradually at the range in which achange in the electric current comes to a constant value as shown inFIG. 1.

SUMMARY OF THE INVENTION

The present invention has been achieved on the basis of our findingsthat the reason why the joining agent shows the time change in theelectric resistance as shown in FIG. 1 is in the fact that anelectroconductive component comprising the ion conductor has theproperty that a rosined ion carrier density or mobility is decreased bymeans of an ion carrier diffusion process into the mother material, andby means of reactions of the ion carrier with the mother material orother joining agent, the oxygen in the atmosphere and the waterresulting from the decomposition of flame.

According to the present invention, there is provided an joining agentfor use in the electric joining method, which comprises anelectroconductive component for providing the electric conductiveproperty shown at the application of electric field and a joiningcomponent for providing a wetability to the ceramic bodies to be jointedat the molten state and a high bonding strength at the curing state,wherein the electroconductive component is selected from the groupconsists of fluoride, chloride and/or oxide ion conductor which forms anion carrier at the preheating range and makes said joining agent have anelectric conductivity higher than that of the ceramics to be jointed atthe electroheating range, and the density or the mobility of the carrierion decreases at the molten state to increase gradually the electricresistance of the joining agent at the molten state.

The ion conductor capable of forming the ion carrier by the preheatingand of increasing gradually the electric resistance of the joining agentat the molten state may be selected from the group consisting offluoride or chloride which forms F⁻ ion or Cl⁻ ion having a highmobility and which is in a solid state at room temperature. Theeffective material is, for example, alkali metal fluoride or chloridesuch as LiF, NaF, KF, LiCl, NaCl or KCl; alkaline earth metal fluorideor chloride such as MgF₂, CaF₂, SrF₂, BaF₂, MgCl₂, CaCl₂ ; or fluorideor chloride of rare earth metal such as SCF₃, YF₃, LaF₃, CeF₃, ScCl₃,YCl₃, LaCl₃. Among them, as the chloride has a deliquescence property,the fluoride is superior in handling. In addition to the abovematerials, the other ion conductor may be selected from the groupconsisting of alkali metal oxides such as Li₂ O, Na₂ O or K₂ O andalkali earth metal oxides such as MgO, or CaO, which can produce cationhaving a rather high mobility.

Among those possible fluoride materials, NaF and CaF₂ are low in thecost and are superior in the reproducibility and the stability.Especially, Sodium fluoride NaF is suitable for the electric conductivecomponent of the joining agent for use in oxide ceramics and calciumfluoride CaF₂ is suitable for the electric conductive component of anjoining agent for joining silicon nitride ceramics. In comparison withthe above fluoride materials, LaF₃, YF₃ or ScF₃ is expensive but acts asa joining component to prevent the decrease in the joining strength dueto the remained Ca and Na elements at the joint layer. Among the aboveoxide materials, the alkaline earth metal oxide such as CaO or MgO isinexpensive and does not produce a poisonous gas such as fluorine gas ina case of fluoride and further has an useful electric conductivity eventhough it is inferior to that of fluoride. Therefore, it is preferableor allowable to use as an electroconductive component, a mixture of morethan two kinds of the above conductive materials so as to have thesuitable electroconductive property in accordance with the applicationfield instead of using one kind of the above conductive material.

A lower limit of the mixing ratio of the conductive component with thejoining component is determined on the basis of an amount to permit theelectric current to flow in a size necessary for producing a sufficientJoule heat during the application of electric field, while a upper limitof the mixing ratio is determined on the basis of an amount not todecrease the strength of the joining agent. In addition, anotherimportance factor to be determined for the mixing ratio is a variationratio of the electric resistance, which varies with the kind and themixing ratio of the conductive material, the kind and the heating degree(of ceramics to be jointed). If the resistance variation ratio of thejoining agent is too small, the movement characteristic of electriccurrent path becomes worse. Hence, it is sometimes difficult to obtainan excellent joined part at the whole of the planes to be jointed. Onthe other hand, if the variation ratio is too large, it may be difficultto permit the electric current to flow due to the resulting highelectric resistance of the joining agent before the sufficient reactionbetween the joining agent and the ceramic bodies to be jointed.Accordingly, in order to carry out the reproducible joining, it isnecessary to select a joining agent having a suitable resistancevariation ratio within the above basic range.

On the other hand, the joining component may be prepared by using, as aglass component, usual oxides such as kaolinite, Al₂ O₃ and SiO₂ and asadditive component, Y₂ O₃, AlN or Si₃ N₄ in a desired mixing ratioaccording to the kind of the ceramic bodies to be jointed. It is alsopossible to use, as an joining component, a transition metal oxide suchas NiO, MnO, ZrO₂, ZnO or TiO₂ in combination with the above joiningcomponent. However, the mixing ratio should be adjusted in a way tosatisfy a good wetability to the ceramic and the necessary joiningstrength.

On the basis of the above aspects, a second object of the presentinvention is to provide a CaF₂ joining agent which is used in theelectric joining method executed, for example, with the highheat-resisting ceramics such as silicon nitride and which is superior inthe reproducible and stable formation of joint part and is provided witha practically usable joining strength at a high temperature.

Further, a third object of the present invention is to provide a NaFjoining agent which is used in the electric joining method for oxideceramics superior in the reproducible and stable formation of the jointpart and is provided with a practically usable joining strength.

It has been found that the joining agent including, as anelectroconductive component, CaF₂ or NaF forms a good reproducibleand-stable joint.

However, the joining agent including CaF₂ or NaF forms a joint layerhaving the Ca or Na element left therein. This causes the joint part tobe inferior in the joining strength, the heat resistance and thecorrosion resistance. In connection with the joining strength at hightemperature, Ca²⁺ ions or Na⁺ ions in the joint layer make a viscosityat a high temperature of the joint layer to be decreased and thus causesthe joining strength at a high temperature to be lowered. For example,Si₃ N₄ ceramic joint part is very low in the joining strength at atemperature higher than 1000° C.

A fourth object of the present invention is to provide a rare earthelement fluoride joining agent system which is used in the electricjoining method and which can improve the joining strength and thecorrosion resistance at the joint part of the ceramic body used as astructure material.

The above-mentioned joining agent of fluoride system is superior in theelectric conductivity but has a disadvantage that the fluorine gasgenerated with the decomposition of the joining agent may weaken theglass structure to decrease the joining strength. The fluorine gas ispoisonous and corrosive and is desirably eliminated from the joiningagent.

Therefore, a fifth object of the present invention is to provide analkali metal oxide joining agent system without any fluorine compound inorder to obtain an joining agent which is used in the electric joiningmethod carried out with the silicon nitride ceramic joining and issuperior in the reproducible and stable joint part formation.

The second object of the present invention is to provide an joiningagent suitable for use in the electric joining method with the siliconnitride ceramic. The joining agent comprises, as a basic component, CaF₂of 10 to 40 weight % Al₂ O₃ more than 10 weight % and the residual ofSiO₂ and as an additives, at least one element of Y₂ O₃ of 10 to 55weight % and Si₃ N₄ of 15 to 45 weight %.

In the above joining agent the proper centent range of CaF₂ is 10 to 40weight %. CaF₂ more than 40 weight % makes the joining strength lower ata high temperature and CaF₂ less than 10 weight % makes the electricconductivity lower and causes the defective joint part.

An use of aluminum oxide results in the following function: Alincorporated with Ca in the joint layer suppresses the action of Ca at ahigh temperature because of 4 coordination of Al and thus increases theviscosity (softening temperature) of the joint layer to elevate thejoining strength at a high temperature.

The proper content range of Al₂ O₃ is more than 10 weight %. The contentof Al₂ O₃ less than 10 weight % can not achieve the above functionmentioned above and decreases the joining strength at a hightemperature.

The addition of silica is to promote the wetability to the ceramics andelevates the joining strength at a room temperature and at a hightemperature when compared with a case having only Al₂ O₃ incorporated.The decrease in the amount of CaF₂ can be compensated by the addition ofSiO₂ in a similar way to the addition of Al₂ O₃.

The incorporated Y₂ O₃ enters the net work structure of silicate(silicate glass) at the joint layer and increases the elasticcoefficient at the joint layer. As a result, the joining agent with Y₂O₃ incorporated increases the joining strength over the joining agentwithout Y₂ O₃. The higher amount of the additive Y₂ O₃ does not alwaysresult in the higher strength of the joint layer. An excess of Y elemententers the joint layer (silicate glass) and destroys the net workstructure of silicate to decrease the softening temperature, whichresults in the decrease in the joining strength at a high temperature.The additive Y element reacts with the other component of the joiningagent to determine the joining strength but the effect to increase thejoint part strength can be achieved by an addition of Y₂ O₃ of 10 to 55weight %.

The addition of Si₃ N₄ makes the joint layer to be oxynitride andchanges the thermal expansion coefficient near to that of the mothermaterial and elevates the elastic coefficient. Further, the softeningtemperature is also elevated and accordingly the strength of the jointlayer is elevated at room temperature and at a high temperature. As aresult, the joining agent with the additive Si₃ N₄ increases the joiningstrength over that without additive Si₃ N₄. An increase or decrease inthe amount of the additive Si₃ N₄ is not in a regular relation with theincrease or decrease in the joining strength. An excess of additive Si₃N₄ makes the electric current flow poor and results in the poor jointlayer. Because it is thought that the material of Si₃ N₄ is very stable.The additive content of Si₃ N₄ requires 15 to 45 weight % to obtain apredetermined effect from various experiments.

The third object of the present invention is to provide the joiningagent system for oxide ceramics and can be achieved by compositionincluding NaF of 5 to 20 weight % and the residual of at least oneelement selected from the group consisting of SiO₂, Al₂ O₃, TiO₂, Y₂ O₃and MgO.

This joining agent is based on NaF, however, NaF of more than 20 weight% make the joinining strength at a high temperature lowered while NaF ofless than 5 weight % makes the electric current flow poor and results inthe defective joint.

The addition of SiO₂ promotes the wetability to the ceramics to bejoined and also compensates the decreased amount of NaF.

The addition of Al₂ O₃ can repair the net work (silicate glassstructure) having a non-bridging oxygen formed by the incorporation ofNa element therein and elevate the softening temperature of the jointlayer. Accordingly, the strength of the joint layer at a hightemperature can be elevated.

MgO is an electroconductive component and can elevate the electricconductivity without increasing the amount of NaF and also make theglass structure stronger at the range of 2.5 to 10 weight %. As aresult, the joining strength at room temperature and a high temperatureis made higher.

The additive Y₂ O₃ enters the silicate net work structure at the jointlayer (silicate glass) and permits the joint layer to have a higherelastic coefficient. Accordingly, the joint strength is made strongerthan that of the joint without Y₂ O₃.

The additive TiO₂ has the same effect as Y₂ O₃.

Further, the fourth object of the present invention is achieved by thefollowing composition: The joining agent includes, as fluorideadditives, rare earth element fluoride such as LaF₃, ScF₃ or YF₃ andachieves the higher strength at a high temperature. The composition isthe rare earth element fluoride more than 15 weight % and the residualof at least one element selected from the group consisting of Al₂ O₃ andSiO₂.

The reason for limiting the rare earth element fluoride to more than 15weight % is that the joining agent having the rare earth elementfluoride less than 15 weight % is in a high electric resistance and doesnot permit the electric current to flow. Even when the electric currentflows, the generation of Joule heat is not uniform. Accordingly,non-melting parts sometimes remain and results in the poor properties.

The joining agent including at least one element selected from the groupconsisting of Al₂ O₃ and SiO₂ as a component for wetability improves thewetability with the ceramics to be joined on melting and results in thesuperior joint.

A composition of about 100 weight % of the rare earth element fluorideLaF₃, ScF₃, or YF₃ can achieve the superior joint. The reason is thatwhen the Si₃ N₄ ceramics are joined by the joining agent, the joiningagent catches SiO₂ produced by a oxidizing reaction of the mothermaterial and the components of the sintering aids for the mothermaterial and accordingly improves the wetability.

The joint part achieved by the joining agent according to the presentinvention is improved in the joint strength, especially the strength ata high temperature and the corrosion resistance in the following reason:When a comparison is made between the IIIA group element (La, Y, and Sc)obtained from the rare earth element fluoride (LaF₃, ScF₃, or YF₃) andgroup of (Ca or Na) obtained from CaF₂ or NaF, La³⁺ ion, Sc³⁺ ion, Y³⁺ion, Ca²⁺ ion or Na⁺ ion destroys the Si--O net work structure in thejoint layer and enters the net work structure as a glass modifying ion.The glass having La³⁺ , Sc³⁺ , or Y³⁺ ion incorporated therein issuperior in the various properties to the glass having Ca²⁺ , or Na⁺ ionincorporated therein.

The higher joint strength comes from the higher packing density of theglass at the joint layer, which makes the strain ratio of glass smallerto improve the Young's modulus. Further, the higher strength at a hightemperature results from the reason that La³⁺, Sc³⁺ or Y³⁺ ion has astronger bonding force with oxygen and improves the softeningtemperature, that is, the viscosity at a high temperature.

Next, the description is directed to a reason why the joining agentaccording to the present invention improves the corrosion resistanceagainst acid and alkali. The corrosion by the acid solution is carriedout by exchanging between H⁺ ion or H₃₀ O⁺ ion in the corrosive solutionand the modifying ions in the net work of glass. Accordingly, La³⁺ ion,Sc³⁺ ion, or Y³⁺ ion has a stronger bonding force with oxygen than Ca²⁺ion or Na⁺ ion and makes it difficult to be exchanged with H⁺ ion or H₃O⁺ ion. This results in the improvement of the corrosion resistance. Thecorrosion with the alkali solution is carried out by destroying thebonding Si--O in the net work in glass with OH⁻ ion in the corrosionsolution. The glass having La³⁺ ion, Sc³⁺ ion or Y³⁺ ion incorporatedtherein increases the packing density and restrains the diffusion of OH⁻ion and improves the corrosion resistance.

The fifth object of the present invention is achieved by using, as aelectric conductive component, the alkali earth metal oxide such as CaOand MgO instead of fluoride. Other component than the electricconductive material can be composed of Al₂ O₃, SiO₂, Y₂ O₃, and/or Si₃N₄.

The joining agents of a CaO system are in a composition of 15 to 50weight % of CaO and a mixing ratio range and a function of the residualof Al₂ O₃, SiO₂, Y₂ O₃, Si₃ N₄ is similar to those of the CaF₂ system.

The joining agents of a MgO system are in a composition of 10 to 45weight % of MgO and a mixing ratio range and a function of the residualof Al₂ O₃, SiO₂, Y₂ O₃, Si₃ N₄ is similar to those of the CaF₂ system.

The joining agents of a MgO system can be improved in the strength at ahigh temperature by adding the transition metal oxide such as NiO, MnO,ZrO₂, ZnO or TiO₂ in a desired ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing a time passage of the variation in theelectric resistance of the joining agent for use in the electric joiningmethod.

FIG. 2 is a block diagram of the joining apparatus for use in theelectric joining method.

THE BEST MODE FOR PRACTICING THE INVENTION

FIG. 2 is a block diagram of an electric joining apparatus for use inthe embodiment. This apparatus comprises an upper sample holding means(3a) and a lower sample holding means (3b), a pressing and positioningcontrol means (10), a gas flame opening for the pre-heating (6a and 6b),electrodes (4a and 4b), electrode moving means (5a and 5b), an electricpower source for heating (8) and various measuring equipments such asvoltmeter, ampere meter or pyrometer(9). The electrode is made oftungsten and is in a bar form or plate form. The electric power sourceis a high voltage electric power source with a drooping characteristicor a high voltage electric power source in a constant current or aconstant voltage type and controls the flowing current or electric powerin a manual or automatic way.

Ceramic bodies are in a block shape for evaluating the strength and isin a size of 15 mm×15 mm×20 mm (a plane to be jointed 15 mm×15 mm). Theroughness of the plane to be jointed is adjusted to be less than 2 μmwith Rmax. A joining agent is a mixture of various powders in a givenmixing ratio and is of a paste form incorporated with organic bindersolved in a solvent such as acetone or toluene. The electric joiningmethod comprises, as a basic process as shown in FIG. 2, the followingsteps of; applying uniformly the joining agent in a paste form to asurface of ceramic bodies to be jointed by a screen printing method,combining the ceramic bodies at the surface to be jointed and settingthe combined ceramic to a holding jig, pre-heating the portion to bejointed to a given temperature with a propane gas flame, applyingelectric voltage across the electrodes after the temperature reaches thegiven value so as to permit the electric current to flow through thejoining agent, moving reciprocally the electrodes in a bar form alongwith the planes to be jointed (when the supplying electric current toelectrodes are in a plate form, the electrodes are in contact with theplanes to be jointed and manage the electric current to flow through allof the planes to be jointed), heating the joining agent up to a giventemperature at a given heating rate under controlling the electriccurrent or the electric power, melting the joining agent, carrying outthe reaction between the ceramic bodies to be jointed and the joiningagent and then cooling, at a given cooling rate, ceramic bodies jointedto each other through the molten joining agent to room temperature tocomplete the joint. The all steps are carried out in the atmosphere ofair. A test piece for strength test (bending test) is in a size of 3 mm×4 mm×40 mm (JIS size) and is obtained by cutting the ceramic bodiesjointed through the joint part in a size of 15 mm×15 mm×40 mm.

CaF₂ Joining Agents for Use in Electric Joining Method

The electric joining method is carried out at the following condition:The used joining agent is in an amount of 50 mg/cm². The pre-heating iscarried out up to a temperature of 800° to 900° C. The flowing electriccurrent through the joining agent is 0.6 to 1 A. The electrode is movedat a rate of 5 cm/min to heat all planes to be jointed. The strengthtest is carried out with the test piece in a JIS form at the followingcondition by using a four points bending test: An upper span is 10 mm,and a lower span is 30 mm. The cross-head speed is 0.5 mm/min. Thetesting result is shown by the average value Mpa (mega pascal) obtainedwith 10 testing pieces subjected to the four points bending test. In thefollowing embodiment, the experimental data and table is described in acollecting manner after description of the invention.

Embodiment 1

In order to confirm the effect of the joining agent according to claim4, the joining agents are prepared by making the mixing ratio of CaF₂and Al₂ O₃ shown in Table 1. The resultant joint parts are tested withthe strength at a room temperature and 1000° C. This test resultindicates that the joining agents including 10 to 40 weight % of CaF₂and 60 to 90 weight % of Al₂ O₃ (testing piece No. attached with symbol*) are provided with the joining strength more than 210 Mpa from roomtemperature to 1000° C.

The joining agents are prepared by including CaF₂, Al₂ O₃ and SiO₂ inaccordance with the mixing ratio shown in Table 2. The resultant jointparts are subjected to the strength test at room temperature and 1000°C. This test result indicates that the joining agents including 10 to 40weight % of CaF2, more than 10 weight % of Al₂ O₃ and more than 10weight % of SiO₂ are provided with the joining strength more than 250Mpa from room temperature to 1000° C.

Embodiment 2

In order to confirm the effect of the joining agent according to claim5, the joining agents are prepared by making the mixing ratio of CaF₂,Al₂ O₃ and Y₂ O₃ shown in Table 3. The resultant joint parts are testedwith the strength at a room temperature and 1000° C. This test resultindicates that the joining agents including 10 to 40 weight % of CaF₂,more than 10 weight % of Al₂ O₃ and 10 to 55 weight % of Y₂ O₃ areprovided with the joining strength more than 300 Mpa from roomtemperature to 1000° C.

The joining agents are prepared by including CaF₂, Al₂ O₃, SiO₂ and Y₂O₃ in accordance with the mixing ratio shown in Tables 4-1 to 4-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 1000° C. This test result indicates that the joiningagents including 10 to 40 weight % of CaF₂, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 10 to 55 weight % of Y₂ O₃ areprovided with the joining strength more than 350 Mpa from roomtemperature to 1000° C.

Embodiment 3

In order to confirm the effect of the joining agent according to claim6, the joining agents are prepared by making the mixing ratio of CaF₂,Al₂ O₃ and Si₃ N₄ shown in Table 5. The resultant joint parts are testedwith the strength at a room temperature and 1000° C. This test resultindicates that the joining agents including 10 to 40 weight % of CaF₂,15 to 45 weight % of Si₃ N₄ and the residual of Al₂ O₃ are provided withthe joining strength more than 300 Mpa from room temperature to 1000° C.

The joining agents are prepared by including CaF₂, Al₂ O₃, SiO₂ and Si₃N₄ in accordance with the mixing ratio shown in Tables 6-1 to 6-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 1000° C. This test result indicates that the joiningagents including 10 to 40 weight % of CaF₂, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 15 to 45 weight % of Si₃ N₄ areprovided with the joining strength more than 350 Mpa from roomtemperature to 1000° C.

Embodiment 4

In order to confirm the effect of the joining agent according to claim7, the joining agent is prepared by making the mixing ratio of 30 weight% of CaF₂, 20 weight % of Al₂ O₃, 25 weight % of Y₂ O₃ and 25 weight %of Si₃ N₄. The strength test with the resultant joint part shows 425 Mpaat room temperature and 422 Mpa at 1000° C. The strength test is carriedout with the joining agent having a composition of 30 weight % of CaF₂,15 weight % of Al₂ O₃, 15 weight % of SiO₂, 20 weight % of Y₂ O₃ and 20weight % of Si₃ N₄. The strength test with the resultant joint partshows 465 Mpa at room temperature and 470 Mpa at 1000° C.

                  TABLE 1                                                         ______________________________________                                        Samples   CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                        Room Temp                                                                              1000° C.                           ______________________________________                                        *1         0     100       --       --                                         2         5     95         92      101                                       *3        10     90        230      228                                       *4        20     80        259      262                                       *5        30     70        283      288                                       *6        40     60        265      212                                        7        45     55        259      137                                        8        50     50        244       71                                       ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Samples                                                                              CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                        SiO.sub.2                                                                          Room Temp  1000° C.                       ______________________________________                                         1      5     10        85    35         54                                    2      5     50        45    61         55                                    3      5     85        10    27         19                                    4     10      5        85   251        213                                   *5     10     10        80   262        258                                   *6     10     45        45   266        271                                   *7     10     80        10   259        258                                    8     10     85         5   208        214                                    9     30      5        65   289        230                                   *10    30     10        60   305        275                                   *11    30     35        35   319        333                                   *12    30     60        10   298        296                                   13     30     65         5   238        244                                   14     40      5        55   263        203                                   *15    40     10        50   267        255                                   *16    40     30        30   289        293                                   *17    40     50        10   301        262                                   18     40     55         5   263        219                                   19     45     10        45   278        192                                   20     45     25        30   290        195                                   21     45     45        10   259        135                                   ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Samples                                                                              CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                        Y.sub.2 O.sub.3                                                                    Room Temp  1000° C.                       ______________________________________                                         1      5     85        10    38         27                                    2      5     60        35    41         61                                    3      5     40        55    55         43                                    4     10     85         5   265        283                                   *5     10     80        10   311        324                                   *6     10     55        35   309        313                                   *7     10     35        55   317        302                                    8     10     30        60   303        215                                    9     20     35        45   328        337                                   *10    20     60        20   331        333                                   *11    30     65         5   278        292                                   *12    30     60        10   313        320                                   13     30     15        55   322        305                                   14     30     10        60   311        223                                   *15    35     10        55   319        303                                   *16    40     55         5   278        234                                   *17    40     50        10   325        310                                   18     40     25        35   341        304                                   19     40     10        50   326        305                                   20     40      5        55   308        244                                   21     45     45        10   231        154                                   22     45     30        25   313        190                                   23     45     10        45   276        145                                   ______________________________________                                    

                  TABLE 4-1                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     10      5      75    10   249      203                                  2     10      5      60    25   285      258                                  3     10      5      30    55   280      233                                  4     10     10      75     5   320      333                                 *5     10     10      70    10   358      362                                 *6     10     10      50    30   365      354                                 *7     10     10      25    55   367      357                                  8     10     10      20    60   341      298                                  9     10     25      60     5   289      304                                 *10    10     25      55    10   372      369                                 *11    10     25      30    35   358      358                                 *12    10     25      10    55   362      353                                 *13    10     40      20    30   363      370                                 *14    10     40      10    40   372      365                                 15     10     40       5    45   330      328                                 *16    10     55      15    20   363      355                                 *17    10     70      10    10   358      371                                 18     10     75      10     5   308      314                                 19     10     75       5    10   305      303                                 ______________________________________                                    

                  TABLE 4-2                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     30      5      55    10   321      275                                  2     30      5      30    35   308      264                                  3     30      5      10    55   311      277                                  4     30     10      55     5   323      315                                 *5     30     10      50    10   364      370                                 *6     30     10      30    30   389      377                                 *7     30     10      10    50   375      368                                  8     30     10       5    55   322      290                                  9     30     30      35     5   317      328                                 *10    30     30      30    10   354      362                                 *11    30     30      20    20   373      380                                 *12    30     30      10    30   369      372                                 13     30     30       5    35   340      335                                 *14    30     50      10    10   363      363                                 15     30     55       5    10   303      309                                 16     30     55      10     5   310      308                                 ______________________________________                                    

                  TABLE 4-3                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     40      5      10    45   328      300                                  2     40      5      25    30   351      282                                  3     40      5      45    10   343      275                                  4     40     10       5    45   339      351                                 *5     40     10      10    40   370      354                                 *6     40     10      25    25   366      354                                 *7     40     10      40    10   358      362                                  8     40     10      45     5   345      322                                  9     40     25       5    30   333      319                                 *10    40     25      10    25   381      358                                 *11    40     25      20    15   379      380                                 *12    40     25      25    10   368      363                                 13     40     25      30     5   328      332                                 *14    40     40      10    10   367      353                                 15     40     45       5    10   309      303                                 16     40     45      10     5   313      321                                 ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                       Si.sub.3 N.sub.4                                                                    Room Temp  1000° C.                       ______________________________________                                         1      5     80       15     29         54                                    2      5     65       30     57         52                                    3      5     50       45     36         23                                    4     10     80       10    245        258                                   *5     10     75       15    310        313                                   *6     10     60       30    316        323                                   *7     10     45       45    304        306                                    8     10     40       50    284        288                                   *9     20     65       15    315        320                                   *10    20     50       30    329        339                                   11     20     30       50    260        272                                   12     30     60       10    289        276                                   *13    30     40       30    337        341                                   *14    30     25       45    318        319                                   15     40     50       10    306        222                                   *16    40     45       15    325        320                                   *17    40     30       30    323        305                                   *18    40     15       45    329        311                                   19     40     10       50    202        219                                   20     45     40       15    269        108                                   21     45     25       30    321        133                                   22     45     10       45    303        145                                   ______________________________________                                    

                  TABLE 6-1                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     10      5      70   15    340      316                                  2     10      5      50   35    352      310                                  3     10      5      35   50    315      312                                  4     10     10      70   10    321      304                                 *5     10     10      65   15    366      358                                 *6     10     10      45   35    355      360                                 *7     10     10      20   50    362      361                                  8     10     10      25   55    265      259                                 *9     10     20      20   50    357      366                                 10     10     20      15   55    254      262                                 11     10     25      10   55    239      244                                 12     10     30      50   15    368      370                                 *13    10     30      45   15    368      370                                 *14    10     30      25   35    378      369                                 *15    10     30      10   50    355      361                                 16     10     35       5   50    323      334                                 *17    10     50      20   20    365      362                                 *18    10     50      10   30    359      362                                 19     10     50       5   35    340      351                                 *20    10     65      10   15    358      355                                 21     10     70      10   10    320      313                                 22     10     70       5   15    302      316                                 ______________________________________                                    

                  TABLE 6-2                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     30      5      50   15    343      299                                  2     30      5      35   30    352      316                                  3     30      5      20   45    333      304                                  4     30     10      50   10    325      313                                 *5     30     10      45   15    370      370                                 *6     30     10      30   30    367      358                                 *7     30     10      15   45    359      365                                  8     30     10      10   50    258      243                                 *9     30     15      10   45    360      358                                 10     20     20       5   45    303      300                                 11     30     30      30   10    321      304                                 *12    30     30      25   15    376      378                                 *13    30     30      20   20    382      373                                 *14    30     30      10   30    380      377                                 15     30     30       5   35    310      306                                 *16    30     45      10   15    365      368                                 17     30     50      10   10    325      331                                 18     30     50       5   15    330      323                                 ______________________________________                                    

                  TABLE 6-3                                                       ______________________________________                                        Sample CaF.sub.2                                                                            Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Si.sub.3 N.sub.4                                                                    Room Temp                                                                              1000° C.                     ______________________________________                                         1     40      5      40   15    344      306                                  2     40      5      25   30    352      327                                  3     40      5      10   45    355      310                                  4     40     10      40   10    343      306                                 *5     40     10      35   15    364      366                                 *6     40     10      20   30    383      373                                 *7     40     10      10   40    360      359                                  8     40     10       5   45    327      339                                  9     40     25      25   10    354      322                                 *10    40     25      20   15    354      351                                 *11    40     25      15   20    374      350                                 *12    40     25      10   25    362      355                                 13     40     25       5   30    341      339                                 *14    40     35      10   15    359      355                                 15     40     40      10   10    323      308                                 16     40     40       5   15    333      315                                 ______________________________________                                    

The joining agents of the above embodiments are applied for the siliconnitride ceramics having a high heat resistance. However, the joiningagents according to the present invention are applicable for ceramicsincluding silicon nitride component such as sialon ceramics.

Further, the joining agents according to the present invention can beprepared by using the compound of alumina Al₂ O₃ and silica SiO₂ such askaolinite (Al₂ O₃. 2 SiO₂. 2 H₂ O) and mullite (3 Al₂ O₃. 2 SiO₂) inplace of a mixture of individual alumina and silica.

In such a way, the joining agents according to the present inventioninclude, as an electric conductive component, CaF₂ and achieve the jointstrength practically usable at high temperature and are very suitablefor joining the ceramic body having a high heat resistance.

NaF Joining Agents for Use in an Electric Joining Method

The following description is directed to the embodiment of claim 8.

The electric joining method is carried out at the following condition:The used joining agent is in an amount of 50 mg/cm². The pre-heating iscarried out up to a temperature of 850° to 900° C. The joining agent atthe joint of ceramic bodies is heated uniformly at all of the joint byan electric current of 0.3 to 2 A. The strength test is carried out in asimilar way to that of the joining agent of CaF₂ system. It is notedthat the experiment data are collectively described at a place behind ofthe detailed description of the invention.

Embodiment 5

In order to confirm the effect of the joining agent according to claim8, the joining agents are prepared by using the mixing ratio of NaF andSiO₂ shown in Table 7. The resultant joint parts are tested with thestrength at a room temperature and 600° C. This test result indicatesthat the joining agents including 5 to 20 weight % of NaF, 80 to 95weight % of SiO₂ (indicated by *) are provided with the joining strengthmore than 100 Mpa from room temperature to 600° C.

The joining agents are prepared by including NaF, Al₂ O₃, and SiO₂ inaccordance with the mixing ratio shown in Table 8. The resultant jointparts are subjected to the strength test at room temperature and 600° C.This embodiment indicates that the joining agents including 5 to 20weight % of NaF, 20 to 60 weight % of Al₂ O₃, and 30 to 70 weight % ofSiO₂ (range having the sample number attached with a symbol *) areprovided with the joining strength more than 150 Mpa from roomtemperature to 600° C.

The joining agents are prepared by including NaF, Al₂ O₃, SiO₂ and MgOin accordance with the mixing ratio shown in Tables 9-1 to 9-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 600° C. This test result indicates that the joiningagents including 5 to 20 weight % of NaF, 20 to 60 weight % of Al₂ O₃,30 to 70 weight % of SiO₂ and 2.5 to 10 weight % of MgO are providedwith the joining strength more than 230 Mpa from room temperature to600° C.

It is noted that Table 10 to 12 indicate the joint part strength at aroom temperature and 600° C. with the joining agents including NaF, Al₂O₃, SiO₂ and the residual of at least one element selected from thegroup consisting of MgO, Y₂ O₃ and TiO₂ in a mixing ratio shown in Table10 to 12.

                  TABLE 7                                                         ______________________________________                                        Samples   NaF    SiO.sub.2 Room Temp                                                                              600° C.                            ______________________________________                                        1         60     40         86       12                                       2         50     50        127       56                                       3         30     70        146       79                                       *4        20     80        208      104                                       *5        10     90        217      122                                       *6         5     95        202      113                                       7          3     97        --       --                                        ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Sample  NaF    Al.sub.2 O.sub.3                                                                        SiO.sub.2                                                                          Room Temp. 600° C.                       ______________________________________                                         1      50     20        30   --         --                                    2      30     40        30   165         98                                   3      30     20        50   172         74                                   4      20     60        20   158        131                                  *5      20     50        30   227        157                                  *6      20     30        50   221        163                                  *7      20     20        60   223        151                                   8      20     10        70   196        119                                   9      10     70        20   --         --                                   *10     10     60        30   238        210                                  *11     10     40        50   226        206                                  *12     10     20        70   229        151                                  13      10     10        80   212        108                                  14       5     65        30   153        162                                  *15      5     60        35   233        213                                  *16      5     42        53   235        202                                  *17      5     25        70   216        162                                  18       5     20        75   201        133                                  19       3     60        37   --         --                                   20       3     47        50    38         42                                  21       3     27        70   --         --                                   ______________________________________                                    

                  TABLE 9-1                                                       ______________________________________                                        Sample NaF    Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           MgO  Room Temp                                                                              600° C.                      ______________________________________                                        *1     5      60      32.5  2.5  256      233                                 *2     5      50      40    5    277      241                                 *3     5      50      35    10   252      238                                  4     5      50      30    15   249      202                                 *5     5      40      52.5  2.5  263      235                                 *6     5      40      50    5    271      253                                 *7     5      40      47.5  7.5  283      246                                 *8     5      40      45    10   259      234                                  9     5      40      40    15   251      193                                 10     5      40      35    20   238      186                                 *11    5      30      60     5   256      232                                 *12    5      30      57.5  7.5  261      240                                 *13    5      20      70     5   250      237                                 *14    5      20      67.5  7.5  253      239                                 *15    5      20      65    10   257      241                                 16     5      35      54.5  2.5  --       --                                  17     3      35      57     5   --       --                                  18     3      30      57    10   68       42                                  ______________________________________                                    

                  TABLE 9-2                                                       ______________________________________                                        Sample NaF     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          MgO   Room Temp                                                                              600° C.                     ______________________________________                                         1     10      70      15   5      68       52                                 2     10      60      25   5     123       89                                 3     10      60      20   10    137      121                                *4     10      50      37.5 2.5   251      233                                *5     10      50      35   5     283      239                                *6     10      40      45   5     296      242                                *7     10      30      57.5 2.5   258      233                                *8     10      30      55   5     273      241                                *9     10      30      50   10    264      238                                10     10      30      45   15    252      218                                11     10      30      40   20    238      193                                12     10      30      30   30    216      166                                *13    10      20      67.5 2.5   252      238                                *14    10      20      65   5     258      242                                *15    10      20      62.5 7.5   261      231                                *16    10      20      60   10    252      237                                17     10      20      55   15    233      162                                18     10      20      50   20    207      153                                19     10      10      75   5     --       --                                 20     10      10      70   10    186       91                                ______________________________________                                    

                  TABLE 9-3                                                       ______________________________________                                        Sample NaF     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          MgO   Room Temp                                                                              600° C.                     ______________________________________                                         1     30      25      40   5     172      146                                 2     30      30      30   10    204      168                                *3     20      -40     37.5 2.5   257      233                                *4     20      40      35   5     278      248                                *5     20      40      30   10    269      252                                *6     20      35      40   5     258      233                                *7     20      35      37.5 7.5   261      241                                *8     20      30      47.5 2.5   256      237                                *9     20      30      45   5     283      242                                *10    20      30      42.5 7.5   271      238                                *11    20      30      40   10    284      230                                12     20      30      35   15    258      212                                *13    20      20      55   5     269      241                                *14    20      20      50   10    253      236                                15     20      20      40   20    241      176                                ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Sample NaF     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          TiO.sub.2                                                                           Room Temp                                                                              600° C.                     ______________________________________                                         1     3       35      57   5     --       --                                  2     3       40      52   5     --       --                                 *3     5       40      50   5     268      255                                 4     5       40      40   15    248      189                                *5     5       35      57.5 2.5   276      257                                *6     5       20      67.5 7.5   253      235                                *7     10      50      37.5 2.5   249      244                                *8     10      40      45   5     283      247                                *9     10      30      50   10    261      242                                10     10      30      45   15    239      222                                *11    10      20      67.5 2.5   268      245                                *12    20      40      35   5     275      250                                *13    20      40      30   10    268      253                                14     20      30      35   15    253      208                                *15    20      20      50   10    253      240                                16     25      40      25   10    259      210                                17     25      30      40   5     250      205                                18     25      20      50   5     238      193                                19     30      40      25   5     215      145                                20     30      30      35   5     211      160                                ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Sample                                                                              NaF     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                     Room Temp                                                                              600° C.                     ______________________________________                                         1     3      35      57    5     --       --                                  2     3      40      25    5     --       --                                  3     5      50      30    15    245      210                                *4     5      40      52.5  2.5   259      241                                *5     5      30      57.5  7.5   270      253                                *6     5      20      70    5     290      245                                *7    10      50      35    5     290      245                                *8    10      30      57.5  2.5   249      240                                *9    10      30      55    5     271      247                                10    10      30      45    15    255      210                                *11   10      20      62.5  7.5   274      242                                *12   20      40      37.5  2.5   255      240                                *13   20      35      40    5     276      245                                *14   20      30      45    5     276      245                                *15   20      20      55    5     264      250                                15    25      40      30    5     231      173                                17    25      30      35    10    240      191                                18    25      20      50    5     228      200                                19    30      30      35    5     220      130                                20    30      25      40    5     222      158                                ______________________________________                                    

                  TABLE 12                                                        ______________________________________                                                                                 Room                                 Sample                                                                              NaF    Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                          Y.sub.2 O.sub.3                                                                    MgO  TiO.sub.2                                                                          Temp  600° C.                 ______________________________________                                        *1     5     50      35   2.5  5    2.5  245   251                            *2    10     45      40   5    2.5  2.5  292   242                            *3    10     35      45   2.5  2.5  5    288   246                            *4    10     30      50   5    2.5  2.5  285   236                            *5    10     35      45   5    5    0    279   261                            *6    10     35      45   0    5    5    284   270                            *7    10     35      45   5    0    5    265   270                            *8    20     40      30   5    5    0    265   252                            *9    20     40      30   2.5  5    2.5  266   244                            10    30     25      35   5    5    0    185   141                            11    30     25      35   2.5  2.5  5    193   162                            ______________________________________                                    

In the above embodiment, the joining agents according to the presentinvention are applied for alumina ceramic but are applicable for anyother oxide ceramics such as mullite ceramic.

Further, the joining agents according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O3. 2 SiO₂. 2 H₂ O) and mullite (3 Al₂ O₃. 2 SiO₂) in place of amixture of individual alumina and silica.

In order to give the joining agents according to the present inventionanother effect or improved effect, it is possible to add the variousadditives besides NaF, Al₂ O₃, SiO₂, MgO, Y₂ O₃, and TiO₂ into thejoining agents according to the present invention. For example, thejoining agents according to the present invention can have nitride suchas Si₃ N₄ or AlN and carbide such as SiC or TiN incorporated therein inorder to include N or C in the glass of the joint layer. Variousproperties of the joint layer are improved by the formation ofoxynitride glass or oxycarbide glass.

In such way, the joining agents according to the present inventioninclude, as an electric conductive component, NaF and achieve the jointpart having a stable strength practically usable at room temperature andhigh temperature and being superior in the sealing property withoutdamaging the mother material are very suitable for joining the oxideceramics.

Joining Agents of Rare Earth Element Fluoride System for Use in anElectric Joining Method

The following description is directed to the embodiment to confirm theeffect of claim 9.

Embodiment 6

An joining agent used is composed of a mixture of 60 weight % of YF₃, 20weight % of Al₂ O₃ and 20 weight % of SiO₂ and is of a paste formincorporated with organic binder solved in a solvent such as acetone ortoluene. A test piece for strength test is prepared by the jointedsilicon nitride ceramic body obtained by joining a couple of siliconnitride ceramic square bars in a size of 15 mm×15 mm×20 mm with thejoining agent in an amount of 50 mg/cm². The silicon nitride ceramicbodies with the joining agent is heated by an electric current of 0.6 to1.0 A for 5 to 10 min under moving the electrode at a rate of 5 cm/min.

A ceramic square bar sample in a size of 3 mm×4 mm×40 mm is obtained bycutting the jointed ceramic bodies. The strength test is carried outwith the test piece at the following condition by using a three pointsbending test: An lower span is 30 mm, and the cross-head speed is 0.5mm/min. The testing result is shown by the average value Mpa (megapascal) obtained with three testing pieces. The resultant strength is420 Mpa at room temperature and is kept nearly to 420 MPa at 1050° C. asshown in Table 13.

                  TABLE 13                                                        ______________________________________                                                                 Unit: MPa                                                        Room Tem-                                                         Main Ingredient                                                                           perature     1000° C.                                                                        1050° C.                             ______________________________________                                        (Conventonal)                                                                             400          350       35                                         CaF--Al.sub.2 O.sub.3 --SiO.sub.2                                             (Invention) 421          419      413                                         Y.sub.2 O.sub.3 --Al.sub.2 O.sub.3 --SiO.sub.2                                ______________________________________                                    

Embodiment 7

A joining agent used here is composed of a mixture of 50 weight % ofScF₃, 25 weight % of Al₂ O₃ and 25 weight % of SiO₂ and the resultantjoint part is subjected to the strength test in a similar way to that ofEmbodiment 6. As shown in Table 14, the result shows a strength of 416MPa which is kept up to 1050° C.

                  TABLE 14                                                        ______________________________________                                                                 Unit: MPa                                                        Room Tem-                                                         Main Ingredient                                                                           perature     1000° C.                                                                        1050° C.                             ______________________________________                                        (Conventonal)                                                                             400          350       35                                         CaF--Al.sub.2 O.sub.3 --SiO.sub.2                                             (Invention) 421          419      413                                         ScF.sub.3 --Al.sub.2 O.sub.3 --SiO.sub.2                                      ______________________________________                                    

The joining agents of the above embodiment are applied for the siliconnitride ceramics having a high heat resistance. However, the joiningagents according to the present invention are applicable for oxideceramics such as Al₂ O₃ or ZrO₂ and non-oxide ceramics such as sialonceramic.

Further, the joining agents according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O₃. 2 SiO₂. 2 H₂ O) and mullite (3 Al₂ O₃. 2 SiO₂) in place of amixture of individual alumina and silica.

In order to give the joining agents according to the present inventionanother effect or improved effect, it is possible to add the variousadditives besides rare earth metal fluoride, Al₂ O₃, and SiO₂, into thejoining agents according to the present invention. For example, thejoining agents according to the present invention can have nitride suchas Si₃ N₄ or AlN and carbide such as SiC or TiN incorporated therein inorder to include N or C in the glass of the joint layer. Variousproperties of the joint layer are improved by the formation ofoxynitride glass or oxycarbide glass

In such way, the joining agents according to the present inventioninclude, as a main ingredient, fluoride of the IIIA group element andAl₂ O₃ and/or SiO₂ and achieve the joint part having a stable strengthpractically usable at room temperature and high temperature and beingsuperior in the corrosion resistance to acid solution and alkalisolution.

Joining Agents of Alkaline Earth Element Oxide System for Use in anElectric Joining Method

The electric joining method and the joint part strength evaluationmethod are carried out in a similar way to that of the joining agents ofCaF₂ system.

Embodiment 8

In order to confirm the effect of the joining agent according to claim10, the joining agents are prepared by using the mixing ratio shown inTables 15 to 20. Referring to Table, the experiment result is described.

The joining agents are prepared by including CaO and Al₂ O₃ inaccordance with the mixing ratio shown in Table 15. The resultant jointparts are subjected to the strength test at room temperature, 900° C.and 1000° C. This test result indicates that the joining agentsincluding 15 to 50 weight % of CaO and 50 to 85 weight % of Al₂ O₃ areprovided with the joining strength more than 200 Mpa from roomtemperature to 1000° C.

The joining agents are prepared by including CaO, Al₂ O₃, and SiO₂ inaccordance with the mixing ratio shown in Table 16. The resultant jointparts are subjected to the strength test at room temperature, 900° C.and 1000° C. This test result indicates that the joining agentsincluding 15 to 50 weight % of CaO, more than 10 weight % of Al₂ O₃, andmore than 10 weight % of SiO₂ are provided with the joint part strengthmore than 250 Mpa from room temperature to 1000° C.

The joining agents are prepared by including CaO, Al₂ O₃, and Y₂ O₃ inaccordance with the mixing ratio shown in Table 17. The resultant jointparts are subjected to the strength test at room temperature and 1000°C. This embodiment indicates that the joining agents including 15 to 50weight % of CaO, more than 10 weight % of Al₂ O₃, and 10 to 55 weight %of Y₂ O₃ are provided with the joint part strength more than 300 Mpafrom room temperature to 1000° C.

The joining agents are prepared by including CaO, Al₂ O₃, SiO₂ and Y₂ O₃in accordance with the mixing ratio shown in Tables 18-1 to 18-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 1000° C. This test result indicates that the joiningagents including 15 to 50 weight % of CaO, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 10 to 55 weight % of Y₂ O₃ areprovided with the joint part strength more than 350 Mpa from roomtemperature to 1000° C.

The joining agents are prepared by including CaO, Al₂ O₃, and Si₃ N₄ inaccordance with the mixing ratio shown in Table 19. The resultant jointparts are subjected to the strength test at room temperature and 1000°C. This embodiment indicates that the joining agents including 15 to 50weight % of CaO, 15 to 45 weight % of Si₃ N₄ and the residual of Al₂ O₃are provided with the joint part strength more than 300 Mpa from roomtemperature to 1000° C.

The joining agents are prepared by including CaO, Al₂ O₃, SiO₂ and Si₃N₄ in accordance with the mixing ratio shown in Tables 20-1 to 20-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 1000° C. This test result indicates that the joiningagents including 15 to 50 weight % of CaO, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 15 to 45 weight % of Si₃ N₄ areprovided with the joint part strength more than 350 Mpa from roomtemperature to 1000° C.

The embodiment indicates that the joining agent including 30 weight % ofCaO, 20 weight % of Al₂ O₃, 25 weight % of Y₂ O₃ and 25 weight % of Si₃N₄ is provided with the joint part strength of 430 Mpa at roomtemperature and 420 MPa at 1000° C.

The embodiment indicates that the joining agent including 30 weight % ofCaO, 15 weight % of Al₂ O₃, is weight % of SiO₂, 20 weight % of Y₂ O₃and 20 weight % of Si₃ N₄ is provided with the joint part strength of459 Mpa at room temperature and 465 MPa at 1000° C.

Embodiment 9

In order to confirm the effect of the joining agent according to claim11, the joining agents are prepared by using the mixing ratio shown inTables 21 to 26. Referring to Table, the experiment result is described.

The joining agents are prepared by including MgO and Al₂ O₃ inaccordance with the mixing ratio shown in Table 21. The resultant jointparts are subjected to the strength test at room temperature and 900° C.This test result indicates that the joining agents including 10 to 45weight % of MgO and 55 to 90 weight % of Al₂ O₃ are provided with thejoining strength more than 250 Mpa from room temperature to 900° C.

The joining agents are prepared by including MgO, Al₂ O₃, and SiO₂ inaccordance with the mixing ratio shown in Table 22. The resultant jointparts are subjected to the strength test at room temperature and 900° C.This test result indicates that the joining agents including 10 to 45weight % of MgO, more than 10 weight % of Al₂ O₃, and more than 10weight % of SiO₂ are provided with the joint part strength more than 300Mpa from room temperature to 900° C.

The joining agents are prepared by including MgO, Al₂ O₃, and Y₂ O₃ inaccordance with the mixing ratio shown in Table 23. The resultant jointparts are subjected to the strength test at room temperature and 900° C.This test result indicates that the joining agents including 10 to 45weight % of MgO, more than 10 weight % of Al₂ O₃, and 10 to 55 weight %of Y₂ O₃ are provided with the joint part strength more than 300 Mpafrom room temperature to 900° C.

The joining agents are prepared by including MgO, Al₂ O₃, SiO₂ and Y₂ O₃in accordance with the mixing ratio shown in Tables 24-1 to 24-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 900° C. This test result-indicates that the joiningagents including 10 to 45 weight % of MgO, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 10 to 55 weight % of Y₂ O₃ areprepared with the joint part strength more than 350 Mpa from roomtemperature to 900° C.

The joining agents are prepared by including MgO, Al₂ O₃, and Si₃ N₄ inaccordance with the mixing ratio shown in Table 25. The resultant jointparts are subjected to the strength test at room temperature and 1000°C. This test result indicates that the joining agents including 10 to 45weight % of MgO, 15 to 45 weight % of Si₃ N₄ and the residual of Al₂ O₃are provided with the joint part strength more than 300 Mpa from roomtemperature to 900° C.

The joining agents are prepared by including MgO, Al₂ O₃, SiO₂ and Si₃N₄ in accordance with the mixing ratio shown in Tables 26-1 to 26-3. Theresultant joint parts are subjected to the strength test at roomtemperature and 900° C. This test result indicates that the joiningagents including 10 to 45 weight % of MgO, more than 10 weight % of Al₂O₃, more than 10 weight % of SiO₂ and 15 to 45 weight % of Si₃ N₄ areprovided with the joint part strength more than 350 Mpa from roomtemperature to 900° C.

The embodiment indicates that the joining agent including 30 weight % ofMgO, 20 weight % of Al₂ O₃, 25 weight % of Y₂ O₃ and 25 weight % of Si₃N₄ is provided with the joint part strength of 415 Mpa at roomtemperature and 430 MPa at 900° C.

The embodiment indicates that the joining agent including 30 weight % ofMgO, 15 weight % of Al₂ O₃, 15 weight % of SiO₂, 20 weight % of Y₂ O₃and 20 weight % of Si₃ N₄ is provided with the joint part strength of465 Mpa at room temperature and 455 MPa at 900° C.

Embodiment 10

In order to confirm the effect of the joining agent according to claim12, the joining agents are prepared by using a mixture of MgO and atransition metal oxide in the mixing ratio shown in Tables 27 to 31 andthe resultant joint parts are subjected to the strength test at roomtemperature and 900° C. It is found that the joining agents of thisembodiment are provided with the strength higher than 200 MPa from roomtemperature to 900° C.

The joining agents including MgO and the transient metal oxide areclearly improved in the joint part strength by adding Si₃ N₄ and Y₂ O₃.For example, a joining agent comprising 50 weight % of MgO, 25 weight %of MnO, and 25 weight % of Y₂ O₃ is provided with the joining strengthof 315 MPa at room temperature and 321 MPa at 900° C. A joining agentcomprising 45 weight % of MgO, 30 weight % of MnO, and 25 weight % ofSi₃ N₄ is provided with the joining strength of 308 MPa at roomtemperature and 310 MPa at 900° C.

                  TABLE 15                                                        ______________________________________                                                                Room                                                  Sample                                                                              CaO       Al.sub.2 O.sub.3                                                                      Temp    900° C.                                                                      1000° C.                         ______________________________________                                        1     10        90      --      --    --                                      2     15        85      272     251   263                                     3     30        70      282     279   281                                     4     40        60      290     253   235                                     5     50        50      273     248   231                                     6     55        45      281     211   111                                     7     100        0      275      92    9                                      ______________________________________                                    

                  TABLE 16                                                        ______________________________________                                                                     Room                                             Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Temp   900° C.                                                                      1000° C.                     ______________________________________                                        1      10      45      45    --     --    --                                  2      15      5       80    291    171    83                                 3      15      10      75    343    337   259                                 4      15      47.5    47.5  335    325   311                                 5      15      75      10    325    331   328                                 6      15      80      5     285    263   271                                 7      30      35      35    341    351   354                                 8      50      5       45    333    143    81                                 9      50      10      40    329    301   255                                 10     50      25      25    337    309   263                                 11     50      40      10    316    305   292                                 12     50      45      5     279    272   281                                 13     55      10      35    342    154    68                                 14     55      22.5    22.5  339    166    69                                 15     55      35      10    318    205   101                                 ______________________________________                                    

                  TABLE 17                                                        ______________________________________                                                                        Room                                          Sample                                                                              CaO       Al.sub.2 O.sub.3                                                                      Y.sub.2 O.sub.3                                                                       Temp  1000° C.                         ______________________________________                                         1    10        80      10      --    --                                       2    10        60      30      --    --                                       3    10        35      55      --    --                                       4    15        80       5      263   269                                      5    15        75      10      329   325                                      6    15        50      35      340   333                                      7    15        30      55      340   320                                      8    15        25      60      336   284                                      9    25        25      50      342   339                                     10    35        35      30      339   335                                     11    35        10      55      341   317                                     12    45        30      25      343   321                                     13    50        45       5      265   258                                     14    50        40      10      321   321                                     15    50        25      25      328   319                                     16    50        10      40      333   315                                     17    50        5       45      331   273                                     18    55        35      10      315   250                                     19    55        20      25      327   235                                     20    55        10      35      329   265                                     ______________________________________                                    

                  TABLE 18-1                                                      ______________________________________                                                                           Room                                       Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                     Temp   1000° C.                     ______________________________________                                        1      15       5      10    70    375    265                                 2      15       5      40    40    381    278                                 3      15       5      70    10    355    286                                 4      15      10      5     70    349    299                                 5      15      10      10    65    388    365                                 6      15      10      40    35    375    371                                 7      15      10      65    10    363    358                                 8      15      10      70    5     325    295                                 9      15      20      10    55    383    372                                 10     15      20      30    35    392    395                                 11     15      40      20    25    388    392                                 12     15      60      15    15    376    383                                 13     15      65      5     15    333    335                                 14     15      65      10    10    366    368                                 15     15      65      15    5     344    337                                 16     15      70      7.5   7.5   328    322                                 ______________________________________                                    

                  TABLE 18-2                                                      ______________________________________                                                                           Room                                       Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                     Temp   1000° C.                     ______________________________________                                        1      30       5      10    55    371    269                                 2      30       5      35    30    374    293                                 3      30       5      55    10    370    304                                 4      30      10      5     55    327    305                                 5      30      10      10    50    375    380                                 6      30      10      20    20    384    377                                 7      30      10      50    10    373    369                                 8      30      10      55    5     328    319                                 9      30      20      25    25    388    383                                 10     30      30      15    25    391    390                                 11     30      30      25    15    379    383                                 12     30      40      15    15    388    385                                 13     30      50      5     15    333    327                                 14     30      50      10    10    365    372                                 15     30      50      15    5     315    325                                 16     30      55      7.5   7.5   326    322                                 ______________________________________                                    

                  TABLE 18-3                                                      ______________________________________                                                                           Room                                       Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                     Temp   1000° C.                     ______________________________________                                        1      50       5      10    35    382    290                                 2      50       5      25    20    377    285                                 3      50       5      35    10    365    288                                 4      50      10      5     35    323    314                                 5      50      10      10    30    378    360                                 6      50      10      20    20    383    358                                 7      50      10      30    10    380    365                                 8      50      10      35    5     331    320                                 9      50      20      15    15    383    359                                 10     50      30      5     15    322    310                                 11     50      30      10    10    365    354                                 12     50      30      15    5     320    295                                 13     50      35      7.5   7.5   338    303                                 ______________________________________                                    

                  TABLE 19                                                        ______________________________________                                        Sample CaO     Al.sub.2 O.sub.3                                                                       Si.sub.3 N.sub.4                                                                    Room Temp 1000° C.                       ______________________________________                                         1     10      45       45    --        --                                     2     10      60       30    --        --                                     3     10      75       15    --        --                                     4     15      35       50    --        --                                     5     15      40       45    341       339                                    6     15      55       30    339       340                                    7     15      70       15    344       347                                    8     15      75       10    295       290                                    9     25      45       30    333       343                                   10     35      25       40    367       350                                   11     35      45       20    360       359                                   12     45      10       45    354       355                                   13     45      25       30    343       348                                   14     50       5       45    --        --                                    15     50      10       40    340       330                                   16     50      20       30    338       329                                   17     50      35       15    322       319                                   18     50      40       10    287       285                                   19     55      20       25    313       233                                   ______________________________________                                    

                  TABLE 20-1                                                      ______________________________________                                                                           Room                                       Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                    Temp   1000° C.                     ______________________________________                                        1      15       5      35    45    361    309                                 2      15       5      50    30    371    300                                 3      15       5      65    15    366    312                                 4      15      10      25    50    --     --                                  5      15      10      30    45    373    365                                 6      15      10      45    30    381    370                                 7      15      10      60    15    382    381                                 8      15      10      65    10    335    330                                 9      15      20      35    30    372    374                                 10     15      30      10    45    383    383                                 11     15      30      25    30    393    390                                 12     15      40      20    25    380    391                                 13     15      50      15    20    375    379                                 14     15      60       5    20    345    333                                 15     15      60      10    15    365    372                                 16     15      60      15    10    319    326                                 17     15      65      10    10    323    315                                 ______________________________________                                    

                  TABLE 20-2                                                      ______________________________________                                                                           Room                                       sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                    Temp   1000° C.                     ______________________________________                                        1      30       5      20    45    374    321                                 2      30       5      35    30    366    315                                 3      30       5      50    15    375    308                                 4      30      10      10    50    --     --                                  5      30      10      15    45    376    371                                 6      30      10      30    30    369    360                                 7      30      10      45    15    375    377                                 8      30      10      50    10    338    341                                 9      30      15      10    45    371    362                                 10     30      15      25    30    396    385                                 11     30      25      20    25    388    377                                 12     30      25      20    25    379    366                                 13     30      35      15    20    383    379                                 14     30      45       5    20    341    322                                 15     30      45      10    15    365    358                                 16     30      45      15    10    332    325                                 17     30      50      10    10    318    323                                 ______________________________________                                    

                  TABLE 20-3                                                      ______________________________________                                                                           Room                                       Sample CaO     Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                    Temp   1000° C.                     ______________________________________                                        1      50       5      10    35    355    303                                 2      50       5      25    20    362    298                                 3      50       5      30    15    358    309                                 4      50      10       5    35    343    311                                 5      50      10      10    30    375    376                                 6      50      10      20    20    380    375                                 7      50      10      25    15    369    365                                 8      50      10      30    10    333    340                                 9      50      20      10    20    375    366                                 10     50      20      15    15    369    365                                 11     50      25       5    20    340    341                                 12     50      25      10    15    377    364                                 13     50      25      15    10    318    315                                 14     50      30      10    10    320    315                                 ______________________________________                                    

                  TABLE 21                                                        ______________________________________                                        Sample   MgO     Al.sub.2 O.sub.3                                                                        Room Temp                                                                              900° C.                            ______________________________________                                        1        100      0        275       35                                       2         5      95        --       --                                        3        10      90        285      279                                       4        20      80        292      282                                       5        35      65        283      276                                       6        45      55        276      260                                       7        50      50        281      205                                       ______________________________________                                    

                  TABLE 22                                                        ______________________________________                                                                         Room                                         Sample  MgO      Al.sub.2 O.sub.3                                                                      SiO.sub.2                                                                             Temp  900° C.                         ______________________________________                                         1       5       10      85      --    --                                      2       5       45      45       11   --                                      3       5       85      10      --    --                                      4      10       5       85      315   243                                     5      10       10      80      319   309                                     6      10       45      45      337   329                                     7      10       80      10      311   309                                     8      10       90      5       281   282                                     9      20       40      40      325   317                                    10      30       35      25      338   315                                    11      40       30      30      335   333                                    12      45       5       50      332   214                                    13      45       10      45      318   314                                    14      45       22.5    22.5    319   324                                    15      45       45      10      321   318                                    16      45       50      5       287   271                                    17      50       10      40      322   119                                    18      50       25      25      319   227                                    19      50       40      10      321   225                                    ______________________________________                                    

                  TABLE 23                                                        ______________________________________                                                                         Room                                         Sample  MgO      Al.sub.2 O.sub.3                                                                      Y.sub.2 O.sub.3                                                                       Temp  900° C.                         ______________________________________                                         1       5       85      10      --    --                                      2       5       65      30      --    --                                      3       5       40      55      --    --                                      4      10       85       5      244   240                                     5      10       80      10      331   329                                     6      10       60      30      328   326                                     7      10       35      55      333   315                                     8      10       30      60      321   255                                     9      20       45      35      349   345                                    10      35       35      30      339   342                                    11      35       10      55      341   321                                    12      40       55       5      276   270                                    13      40       50      10      323   333                                    14      40       40      30      330   328                                    15      40       10      50      332   319                                    16      40        5      55      318   266                                    17      45       45      10      315   263                                    18      45       25      30      324   275                                    19      45       10      45      320   269                                    ______________________________________                                    

                  TABLE 24-1                                                      ______________________________________                                                                            Room                                      Sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                      Temp  900° C.                      ______________________________________                                        1      10      5       75    10     357   314                                 2      10      5       55    30     361   298                                 3      10      5       30    55     363   300                                 4      10     10       75    5      332   321                                 5      10     10       70    10     365   358                                 6      10     10       45    35     376   365                                 7      10     10       25    55     378   377                                 8      10     10       20    60     356   310                                 9      10     25       30    35     389   378                                 10     10     25       10    55     387   369                                 11     10     45       25    30     391   390                                 12     10     55       15    20     385   388                                 13     10     70       15    5      313   308                                 14     10     70       10    10     361   359                                 15     10     70       5     15     333   334                                 16     10     75       7.5   7.5    303   310                                 ______________________________________                                    

                  TABLE 24-2                                                      ______________________________________                                                                            Room                                      Sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                      Temp  900° C.                      ______________________________________                                        1      30      5       10    55     365   303                                 2      30      5       35    30     357   289                                 3      30      5       55    10     361   302                                 4      30     10       5     55     319   311                                 5      30     10       10    50     371   372                                 6      30     10       20    20     370   365                                 7      30     10       50    10     366   360                                 8      30     10       55    5      320   323                                 9      30     20       25    25     381   390                                 10     30     30       15    25     392   378                                 11     30     30       25    15     388   382                                 12     30     40       15    15     390   386                                 13     30     50       5     15     323   313                                 14     30     50       10    10     369   370                                 15     30     50       15    5      310   313                                 16     30     55       7.5   7.5    299   295                                 ______________________________________                                    

                  TABLE 24-3                                                      ______________________________________                                                                            Room                                      sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Y.sub.2 O.sub.3                                                                      Temp  900° C.                      ______________________________________                                        1      45      5       10    40     381   293                                 2      45      5       25    25     377   303                                 3      45      5       40    10     372   305                                 4      45     10       5     40     331   329                                 5      45     10       10    35     380   378                                 6      45     10       20    25     396   389                                 7      45     10       35    10     385   386                                 8      45     10       40    5      329   323                                 9      45     20       15    20     379   377                                 10     45     30       10    15     381   375                                 11     45     35       5     15     323   311                                 12     45     35       10    10     373   359                                 13     45     35       15    5      319   308                                 14     45     40       7.5   7.5    305   316                                 ______________________________________                                    

                  TABLE 25                                                        ______________________________________                                                                         Room                                         Sample  MgO      Al.sub.2 O.sub.3                                                                      Si.sub.3 N.sub.4                                                                      Temp  900° C.                         ______________________________________                                         1       5       50      45      --    --                                      2       5       65      30      --    --                                      3       5       80      15      --    --                                      4      10       40      50      --    --                                      5      10       45      45      343   339                                     6      10       60      30      351   348                                     7      10       75      15      309   315                                     8      10       80      10      288   275                                     9      25       55      20      329   331                                    10      25       35      40      341   340                                    11      35       35      30      333   329                                    12      45        5      50      --    --                                     13      45       10      45      324   318                                    14      45       25      30      327   315                                    15      45       40      15      325   322                                    16      45       45      10      297   275                                    17      50       10      40      315   257                                    18      50       20      30      309   261                                    19      50        5      45      303   245                                    ______________________________________                                    

                  TABLE 26-1                                                      ______________________________________                                                                            Room                                      Sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                     Temp  900° C.                      ______________________________________                                         1     10      5       40    45     370   305                                  2     10      5       55    30     372   315                                  3     10      5       70    15     368   308                                  4     10     10       30    50     --    --                                   5     10     10       35    45     373   369                                  6     10     10       50    30     381   375                                  7     10     10       65    15     375   365                                  8     10     10       70    10     332   328                                  9     10     25       25    40     395   387                                 10     10     35       25    30     389   383                                 11     10     35       10    45     371   385                                 12     10     45       15    30     381   386                                 13     10     55       15    20     375   379                                 14     10     65        5    20     331   313                                 15     10     65       10    15     365   358                                 16     10     65       15    10     322   315                                 17     10     70       10    10     308   313                                 ______________________________________                                    

                  TABLE 26-2                                                      ______________________________________                                                                            Room                                      Sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                     Temp  900° C.                      ______________________________________                                        1      30      5       20    45     368   319                                 2      30      5       35    30     369   307                                 3      30      5       50    15     373   314                                 4      30     10       10    50     --    --                                  5      30     10       15    45     389   385                                 6      30     10       30    30     394   390                                 7      30     10       45    15     375   382                                 8      30     10       50    10     321   318                                 9      30     15       10    45     369   371                                 10     30     15       25    30     380   375                                 11     30     25       20    25     375   373                                 12     30     25       20    25     375   370                                 13     30     35       15    20     361   375                                 14     30     45        5    20     319   309                                 15     30     45       10    15     361   359                                 16     30     45       15    10     299   312                                 17     30     50       10    10     309   312                                 ______________________________________                                    

                  TABLE 26-3                                                      ______________________________________                                                                            Room                                      Sample MgO    Al.sub.2 O.sub.3                                                                       SiO.sub.2                                                                           Si.sub.3 N.sub.4                                                                     Temp  900° C.                      ______________________________________                                        1      45      5       10    40     371   294                                 2      45      5       20    30     365   315                                 3      45      5       35    15     369   310                                 4      45     10        5    40     332   312                                 5      45     10       10    35     381   383                                 6      45     10       20    25     379   372                                 7      45     10       30    15     384   376                                 8      45     10       35    10     329   317                                 9      45     20       10    25     395   396                                 10     45     20       15    20     392   387                                 11     45     30       15    10     318   315                                 12     45     30       10    15     372   359                                 13     45     30        5    20     322   321                                 14     45     35       10    10     312   318                                 ______________________________________                                    

                  TABLE 27                                                        ______________________________________                                        Sample    MgO    NiO       Room Temp                                                                              900° C.                            ______________________________________                                        1         35     65        --       --                                        2         40     60        219      225                                       3         60     40        236      222                                       4         75     25        238      241                                       5         90     10        244      233                                       6         95      5        221       85                                       ______________________________________                                    

                  TABLE 28                                                        ______________________________________                                        Sample    MgO    MnO       Room Temp                                                                              900° C.                            ______________________________________                                        1         20     80        --       --                                        2         25     75        247      250                                       3         50     50        237      246                                       4         60     40        275      255                                       5         70     30        280      293                                       6         80     20        248      261                                       7         85     15        255       36                                       ______________________________________                                    

                  TABLE 29                                                        ______________________________________                                        Sample    MgO    SrO.sub.2 Room Temp                                                                              900° C.                            ______________________________________                                        1         25     75        --       --                                        2         30     70        267      273                                       3         50     50        296      281                                       4         70     30        297      290                                       5         90     10        291      289                                       6         95      5        275       71                                       ______________________________________                                    

                  TABLE 30                                                        ______________________________________                                        Sample    MgO    ZnO       Room Temp                                                                              900° C.                            ______________________________________                                        1         35     65        --       --                                        2         40     60        223      236                                       3         60     40        250      248                                       4         75     25        251      266                                       5         90     10        238      222                                       6         95      5        245       83                                       ______________________________________                                    

                  TABLE 31                                                        ______________________________________                                        Sample    MgO    TiO.sub.2 Room Temp                                                                              900° C.                            ______________________________________                                        1         45     55        --       --                                        2         50     50        275      282                                       3         65     35        284      280                                       4         80     20        299      288                                       5         90     10        265      275                                       6         95      5        277       42                                       ______________________________________                                    

The joining agents of the above embodiment are applied for the siliconnitride ceramics having a high heat resistance. However, the joiningagents according to the present invention are applicable for ceramicsincluding a silicon nitride component such as sialon ceramics.

Further, the joining agents according to the present invention can beprepared by using the compound of alumina and silica such as kaolinite(Al₂ O₃. 2 SiO₂. 2 H₂ O) and mullite (3 Al₂ O₃. 2 SiO₂) in place of amixture of individual alumina and silica.

In such a way_(t) the joining agents according to the present inventioninclude, as an electric conductive component, alkaline earth elementoxide and achieve the joint part strength practically usable at hightemperature and are very suitable for joining the ceramic body having ahigh heat resistance.

The joining agents shown in examples 1 to 10 includes, as an electricconductive component, one kind of material. However, it is possible touse more than two kinds of electric conductive materials.

In the above embodiments, the electric joining process with the joiningagents according to the present invention is carried out in air but canbe carried out in an inert gas such as Ar gas or in N₂ gas.

The effect of the joining agents according to the present invention isconfirmed by a basic electric joining method. The joining agentsaccording to the present invention are applicable for the improvedjoining methods which are being applied for another application(PCT/JP91/00560) and are aimed at the joining of ceramic body in a largesize or in a long size.

What is claimed is:
 1. A joining agent which is used for joining ceramicbodies by an electric joining method comprising:a composition of: (a) anelectric conductive component effective for providing an electricconductivity to said composition at an electric current supplying time;and (b) a joining component for providing an effective wetability to theceramic bodies at the molten state of the joining agent and an effectivejoining strength in the solidified state; wherein said electricconductive component is an ion conductor selected from the groupconsisting of fluorides, chlorides, alkali metal oxides and alkalineearth metal oxides and is selected so as to form carrier ions duringpro-heating which provide said joining agent with an electricconductivity higher than that of the ceramic bodies at the electriccurrent supplying time, whereby said electric conductive component andsaid joining component are selected in effective amounts such that theelectric resistance of said joining agent increases gradually at saidmolten state by decreasing the density or the mobility of said carrierions; wherein said composition comprises 10 to 40 weight % of CaF₂, assaid electric conductive component and more than 10 weight % of Al₂ O₃,15 to 45 weight % of Si₃ N₄ and the residual of SiO₂ as said joiningcomponent.
 2. A joining agent which is used for joining ceramic bodiesby an electric joining method comprising:a composition of: (a) anelectric conductive component effective for providing an electricconductivity to said composition at an electric current supplying time;and (b) a joining component for providing an effective wetability to theceramic bodies at the molten state of the joining agent and an effectivejoining strength in the solidified state; wherein said electricconductive component is an ion conductor selected from the groupconsisting of fluorides, chlorides, alkali metal oxides and alkalineearth metal oxides and is selected so as to form carrier ions duringpre-heating which provide said joining agent with an electricconductivity higher than that of the ceramic bodies at the electriccurrent supplying time, whereby said electric conductive component andsaid joining component are selected in effective amounts such that theelectric resistance of said joining agent increases gradually at saidmolten state by decreasing the density or the mobility of said carrierions; wherein said composition comprises 10 to 40 weight % of CaF₂, assaid electric conductive component and more than 10 weight % of Al₂ O₃,10 to 55 weight % of Y₂ O₃, 15 to 45 weight % of Si₃ N₄ and the residualof SiO₂ as said joining component.
 3. A joining agent which is used forjoining ceramic bodies by an electric joining method comprising:acomposition of: (a) an electric conductive component effective forproviding an electric conductivity to said composition at an electriccurrent supplying time; and (b) a joining component for providing aneffective wetability to the ceramic bodies at the molten state of thejoining agent and an effective joining strength in the solidified state;wherein said electric conductive component is an ion conductor selectedfrom the group consisting of fluorides, chlorides, alkali metal oxidesand alkaline earth metal oxides and is selected so as to form carrierions during pre-heating which provide said joining agent with anelectric conductivity higher than that of the ceramic bodies at theelectric current supplying time, whereby said electric conductivecomponent and said joining component are selected in effective amountssuch that the electric resistance of said joining agent increasesgradually at said molten state by decreasing the density or the mobilityof said carrier ions; wherein said composition comprises more than 15weight % of at least one compound selected from the group consisting ofScF₃ and YF₃ as said electric conductive component and the residual ofat least one compound selected from the group consisting of Al₂ O₃ andSiO₂ as said joining component.